Various efforts have hitherto been made to increase the functionality of polymer compounds. For example, in one approach currently used to increase the refractive index of polymer compounds, aromatic rings, halogen atoms or sulfur atoms are introduced onto the compounds. Of such compounds, episulfide polymer compounds and thiourethane polymer compounds, both of which have sulfur atoms introduced thereon, have been commercialized as high-refractive index lenses for eyeglasses.
The most effective way to achieve even higher refractive indices in polymer compounds is known to involve the use of inorganic metal oxides.
For instance, a method for increasing the refractive index by using a hybrid material composed of a siloxane polymer mixed with a material containing small dispersed particles of zirconia, titania or the like has been disclosed (Patent Document 1).
A method in which a condensed ring skeleton having a high refractive index is introduced onto portions of a siloxane polymer has also been disclosed (Patent Document 2).
In addition, numerous attempts have been made to impart heat resistance to polymer compounds. Specifically, it is well known that the heat resistance of polymer compounds can be improved by introducing aromatic rings onto the molecule. For example, polyarylene copolymers with substituted arylene recurring units on the backbone have been disclosed (Patent Document 3). Such polymer compounds show promise primarily in use as heat-resistant plastics.
Melamine resins are familiar as triazine resins, but have very low decomposition temperatures compared with heat-resistant materials such as graphite.
The heat-resistant organic materials composed of carbon and nitrogen that have been used up until now are for the most part aromatic polyimides and aromatic polyamides. However, because these materials have linear structures, their heat-resistance temperatures are not all that high.
Triazine-based condensation materials have also been reported as nitrogen-containing polymer materials having heat resistance (Patent Document 4).
Lately, in the development of electronic devices such as liquid-crystal displays, organic electroluminescence (EL) displays, optical semiconductor (LED) devices, solid-state image sensors, organic thin-film solar cells, dye-sensitized solar cells and organic thin-film transistors (TFTs), there has arisen a need for high-performance polymer materials.
The specific properties desired in such polymer materials include (1) heat resistance, (2) transparency, (3) high refractive index, (4) high solubility, (5) low volume shrinkage, and (6) weather resistance.
The inventors earlier discovered that hyperbranched polymers containing recurring units with a triazine ring and an aromatic ring have a high refractive index, are capable of achieving high heat resistance, high transparency, high refractive index, high solubility and low volume shrinkage with the polymer alone, and are thus suitable as film-forming compositions in the manufacture of electronic devices (Patent Document 5). When cured films produced from such compositions are employed as high-performance films in electronic devices, weather resistance such as stability to ultraviolet light is desired. Yet, there remains room for further improvement in this regard in thin-films obtained from the compositions of Patent Document 5.